Studies are continuing on the role of HLA gene projucts in recognition of foreign antigen by human T cells. Studies in this project include analysis of T cell responses to the hapten TNP and to influenza virus (previously designated project Z01-CB-05078 I) The principal effector mechanism under investigation is cell-mediated cytotoxicity, but proliferation is also used as measurement of T cell response. Population and family studies of influenze specific CML indicate considerable diversity among serologically indistinguishable molecules, and suggest that individual HLA-A3 molecules may xpress more than one site for recognition by MHC restricted T cells. The new pair of Bw44 related HLA antigens which have been identified (Z02-CB-05101-02 I) have been analyzed for their ability to function as restriction antigens for influenza-specific CTL. In contrast to studies of other HLA antigens, the "public" antigen Bw44 appears to function more effectively as a restriction antigen than its "private" counterparts 44.1 and 44.2 Preliminary collaborative studies indicate thatthe SB2 antigen (Z01-CB-05101-02 I) can restrict recognition of influenza specific proliferating T cells.